Method and a package for extending the shelf life of a food

ABSTRACT

A method of achieving extended shelf life for a food includes enclosing the food in a discrete container of flexible or foldably formable material, wherein the shape of the container includes predefined crease lines for enabling the formation of the container into at least the following two container positions: a) a first container position obtained by the formation of folds along predefined crease lines such that opposing side wall panels of the container are arranged in relation to one another such that the distance between the side wall panels defines a first distance and b) a second container position obtained without the formation of folds along the predefined crease lines such that opposing side wall panels of the container are arranged in relation to one another such that the distance between the side wall panels defines a second distance. The first distance between the side wall panels is less than the second distance between the side wall panels. The method further includes treating the food in the container with heat in a treatment chamber while the container maintains the first container position, and thereafter, raising the container to the second container position. The second position of the container corresponds to that form under which the container is distributed, sold or used.

This application is 371 of PCT/SE96/00880 filed on Jul. 1, 1996.

TECHNICAL FIELD

The present invention relates to a method of heat treating a pumpablefood for the purpose of extending its shelf life, such treatment beingcarried out in a treatment chamber, preferably an autoclave, once thefood has been enclosed in a container of flexible or foldably formablematerial. The present invention also relates to a container and anapparatus for reducing the method into practice.

BACKGROUND ART

It has long been known in the art that the shelf life of a food may beextended by subjecting the food to heat treatment which is so thoroughthat bacteria, fungi and other micro-organisms present in the food arekilled-off, neutralised or reduced in number. In order to achievecomplete sterilization, the treatment must be carried out under suchforms that it is certain that all parts of the treated product areheated to such an elevated degree and for such a length of time as arerequired for complete destruction or deactivation of the micro-organismsin the product.

Different types of food products require different forms of treatment.For example, milk or lactic products must be subjected to more extensivetreatment (higher temperature and/or longer treatment time) than, forexample, acidic products such as fruit juices of different types. Thereason for this is that the basic preconditions for growth of themicro-organisms in an acidic environment are substantially poorer thanif the environment is basic or neutral. By way of example, mention mightbe made of the fact that milk can be sterilized by means of a shortheating time up to approximately 140° C., for a few (4 to 10) seconds,while on the other hand orange juice can be treated to completesterilization at a temperature of approximately 100° C. and less, in atreatment time of a few seconds or a few tenths of a second. Sinceextensive heating of food products generally gives rise to adeterioration in flavour and also a deterioration in the quality of thefinished product, attempts are made in the art to restrict the effectsof the heat to as little as possible, which is generally achieved byheating to a relatively high temperature for a short time.

In that case when the product which is to be heat-treated is aqueous (asis the case in milk and juice), heating to a temperature above 100° C.cannot take place without the water in the product being caused to boil,unless the treatment takes place in an enclosed space in which an excesspressure can be maintained and the boiling point of the product canthereby be raised. Such an apparatus goes under the general title of anautoclave, and an autoclave is thus an apparatus which comprises anenclosed treatment chamber in which both temperature and pressure may becontrolled and regulated. One of the drawbacks inherent in autoclavingis that the treatment is largely carried out intermittently for a numberof objects inserted in the autoclave (so-called batch treatment), andthat the treatment time depends on the length of time that elapses toensure total treatment, i.e. by heating of the product placed in theautoclave.

Since heat is to be supplied to the product through its enclosing orpackaging material, and be led in to the central regions of the product,it is advantageous to keep the thermal transfer path to the centralareas of the product as short as possible in order thereby to limit thetotal heating time of the product. The product must, thus, be as thin orflat as possible during the heat treatment, i.e. have a least possibleextent in one dimension, but this requirement on the product and itspackaging form generally runs counter to other requirements placed onthe packaging container, for example that it be of a configuration thatmakes it easy to distribute and store, and that it must be able to standupright on its own on a flat substrate without tipping over.

In the present case, this problem is solved in the manner apparent fromthe appended claims.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

One preferred embodiment of the present invention will now be describedin greater detail hereinbelow, with particular reference to theaccompanying schematic Drawings, in which:

FIG. 1 shows part of a packaging material web which is provided with acrease line pattern facilitating folding;

FIG. 2 schematically illustrates how a web according to FIG. 1 is formedand filled to make closed packaging containers;

FIG. 3 shows a closed packaging container in the flat-laid or reducedthickness state;

FIG. 4 schematically illustrates an autoclave or heat treatment chamberin which the packaging containers are heated under pressure; and

FIG. 5 shows the final packaging container which is filled withsterilized or partially sterilized contents.

DESCRIPTION OF PREFERRED EMBODIMENT

As was mentioned above, autoclave heat-treatment can be carried out on aproduct which has been enclosed in a formable container consisting offlexible and/or foldable material, for example plastic-coated paper withor without layers of metal foil or other barrier material for gases andaroma substances. The packaging material may also be produced from aplastic film laminate comprising, for example, carrier or core layers ofpolypropylene, polyester or similar heat resistant plastic material.

In the present case, it will be assumed that the treated and packedproduct consists of milk and the object of the present invention is tocreate a package containing a bacteria-reduced or sterile product, andto ensure that substantially prolonged shelf-life has been imparted tothe product once it has been packed and treated together with is hostpackaging.

The above-defined technical problem is solved in accordance with thepreferred embodiment of the present invention in that, as shown in FIG.1, a web of packaging material 9 is produced by lamination of carrierlayers of paper or plastic, inner and outer sealing layers ofthermoplastic, for example polyethylene and, where applicable, barrierlayers of metal foil, barrier plastic (such as a copolymer of ethyleneand vinyl alcohol, known as EVOH) or plasma deposited glass material. Aswill be apparent from FIG. 1, the web 9 is divided into fields or panels7, 8 and 10 by longitudinal and transverse so-called crease lines 4. Inthe finished package 1;14, the panels 7 and 8 constitute the wallsurfaces of the package, while the panels 10 constitute sealing panelsalong which the packaging material is united in tight and mechanicallydurable seams or joints inside-to-inside or in overlap joint in thatmutually abutting material surfaces are heated to melting point at thesame time as they compressed towards one another so that abuttingsealing panels are caused to melt and fuse together.

The web 9 may be formed into a tube in that the longitudinal web edgesare united to one another in a continuous overlap seal along the sealingpanel 10 in the manner which is illustrated schematically in FIG. 2. Asis apparent from FIG. 2, the web 9 is unwound from a magazine reel 17and is passed over a bending roller 19 in order to be transformed, as itmoves downwards, into a tube 20 which is sealed along a longitudinalseam. The tube 20 is filled with its intended contents through thefiller pipe 21 and, in the tube, the filling level is marked byreference numeral 22. Under continuous movement and filling, the lowerportion of the tube 20 is formed into packaging containers 1 of theintended configuration with the aid of sealing and forming devices 23which are brought into engagement with the tube 20 and, in synchronousmovement with the advancement of the tube, seal off the filled lowertube portion by flat-pressing in the transverse zones 10 of thepackaging material. Advancement of the packaging material web 9 issynchronised with the movement of the sealing and forming devices 23 sothat the transverse seals of the tube 20 are effected in register withthe field- or panel-forming crease line pattern of the packagingmaterial web 9. As was mentioned previously, the above crease linepattern comprises longitudinal and transverse crease lines 4 whichfacilitate forming of the package 1 by folding along the crease lines 4.

After sealing and forming of the package, a somewhat "cushion-shaped"package 1 is formed whose outer edges are constituted by the fold linesalong the crease lines 3 and the sealing fins 2 that are formed when thepackaging container 1 is, after sealing and forming, severed from thetube 20 by incisions in the transverse seals 10. The illustrated packagedisplays in itself an "undefined" cushion shape and this may also beproduced from prefabricated and punched packaging blanks which areraised and filled individually, but in the embodiment described here,the separated packages 1 have been given hexagonal cross section by foldformation along the crease lines 3 and 4 in the manner illustrated inFIG. 3, where the longitudinal overlap seam or joint of the packagecarries reference numeral 5.

In the manner schematically intimated in FIG. 1, the above-disclosed"primary" packaging container 1 is inserted into an autoclave 18. In theautoclave, the pressure and temperature are raised in the space 11 atthe same time as the packages 1 are compressed by means of devicesoperating with the aid of a drive unit 24 (e.g. pressure cylinders) andassociated piston rods 16. The devices or pressure plates 15 aredisplaced by means of their drive unit 24 from an inactive position 15'to an active position 15 in which the packages 1 are compressed togetherso that their thickness is reduced to a minimum, taking into account thevolume of the contents and the surface of the packaging material, andfinally the configuration of the package proper. The pressure againstthe packages 1 must not, of course, exceed the level that joint seamsand packaging material can withstand, but the thickness of the packageshould be reduced to a minimum.

The packaging container 1 is dimensionally stable in that it is held inits "flat-pressed" thickness-reduced position while the contents,together with the packaging material, are heated to a temperature which,in autoclave treatment, exceeds 100° C. Given that the pressure in thechamber 11 is maintained above atmospheric, the boiling point of thecontents in the packaging container 1 will be raised so that thecontents can be heated to a temperature exceeding 100° C. without therisk of steam forming in the package. By flattening the package, heatingproceeds more rapidly than if the package had retained greaterthickness, and heat can be supplied with the aid of the pressure plates15.

Although this is illustrated in FIG. 4, it is not unconditionallynecessary to compress the packages 1 with the aid of pressure plates 15to maintain a dimensionally stable package. As is apparent from FIGS. 3and 5, the "cushion-shaped" package 1 which is illustrated in FIG. 3 isof lesser thickness than the package 1 which is shown in FIG. 5. This isbecause the closed package which is shown in FIG. 3 has not been givenits ultimate form, but displays a flattened "cushion" shape. As isapparent from FIGS. 1, 3 and 5, the packages 1 and the packagingmaterial web 9 are provided with an extra crease line 3 which is notemployed as a folding line in the finished package 1 in accordance withFIG. 5. However, the crease line 3 does have an important function tofulfil in that folding of the packaging wall along this crease lineentails that the packaging container 1 can be given a flatter shape (seeFIG. 3), even if the packaging material is relatively rigid. Thepresence of the crease line or crease lines 3 thus implies that theinventive concept as herein disclosed may be applied in an efficientmanner with or without the aid of the previously described pressureplates 15.

The above-described embodiment relates to the case when the package isintended to be formed by folding along crease lines previously providedin the packaging material. The method according to the present inventionmay, however, also advantageously be applied in cases when the packagein itself has an indeterminate geometric shape, for example a bag shapeor a cushion shape--the decisive factor being that the closed packagewith contents is heat-treated while the greatest possible "flattened" or"laid-out" shape is imparted to the package. Another precondition isthat the package, after the heat treatment, is reformed so as to assumethat form which is desirable for distribution and handling of thepackage, and this, for example in "geometrically shapeless" bag orcushion packages, can be achieved in that the package, after heattreatment and cooling, is inserted in an outer, rigid packaging, forinstance an outer carton, whereupon the cushion package is automaticallyshaped to correspond with the defining walls of the outer carton.Naturally, it is also conceivable that the above-mentioned cushion orbag of indeterminate geometric shape can (at least partly) be givendeterminate shape by folding in of a part of the surface of the cushionor bag so as to form a substantially planar "standing surface" while theremaining parts of the package are of a shape which is substantiallygeometrically indeterminate.

According to one embodiment of the invention, the package may, forexample, consist of a plurality of sheets or webs which may be edgesealed, filled and finally sealed, in which event the sealing joint orseam may consist of an inherently closed sealing seam which liessubstantially in one plane and which unites the above-mentioned sheetsor webs. In the event that the packages are manufactured from one web,the individual packages may be separated by incisions through thesealing zones which extend between the edge portions of the webs. Inthis case, there will thus be obtained a cushion-shaped package with thesealing seam or joint designed as a "frame" which forms the outerdefining lines of the cushion in the plane of the sealing joint. Whenlaid on a substrate with the plane of the sealing joint substantially inthe horizontal, such a package will show a tendency to adopt a positionwhich minimises the thickness of the cushion, implying that the cushion,when placed in an autoclave, assumes a position which is favourable forheat treatment. As was previously mentioned, the above-disclosedcushion-shaped package may be given a more permanent and determinategeometric form by inward flap folding for the formation of a standingsurface, or alternatively the bag may be provided with a rigidifyinglabel or bandoleer strip. Alternatively, it may be inserted into anouter carton or package possessing rigid walls and a determinategeometric shape.

It has proved that, by applying the method according to the presentinvention, it is possible to substantially reduce the heat treatmenttime for foods packed in closed packages and, depending upon the formand appearance of the packaging container and the nature of thepackaging material, the treatment time may be reduced by between 10 and40 percent, which implies major economic advantages and, in addition,increased reliability that all parts of the treated food are exposed tothe intended bacteria-destruction effect.

The method may be employed for treating both free-flowing and viscousfoods and also for liquid foods such as soups which contain solidparticles (for example peas, beans, small pieces of meat, etc.).

The present invention should not be restricted to that described aboveand shown on the Drawings, many modifications being conceivable withoutdeparting from the spirit and scope of the appended claims.

What is claimed is:
 1. A method of achieving extended shelf life for afood, said method comprising:enclosing the food in a discrete containerof flexible or foldably formable material, wherein the shape of saidcontainer includes predefined crease lines for enabling the formation ofsaid container into at least two container positions, a) a firstcontainer position obtained by the formation of folds along predefinedcrease lines such that opposing side wall panels of the container arearranged in relation to one another such that the distance between theside wall panels defines a first distance, and a layer thickness of theenclosed food defines a first food layer thickness, and b) a secondcontainer position obtained without the formation of folds along saidpredefined crease lines such that opposing side wall panels of thecontainer are arranged in relation to one another such that the distancebetween the side wall panels defines a second distance, and the layerthickness of the enclosed food defines a second food layer thickness,treating the food in the discrete container with heat in a treatmentchamber while said container maintains the first container position, andthereafter, raising said container to the second container position,said second position of the container corresponding to that form underwhich the container is distributed, sold or used; wherein the firstdistance between the side wall panels and the first food layer thicknessis less than the second distance between the side wall panels and thesecond food layer thickness.
 2. The method as claimed in claim 1,wherein the container which is produced from the packaging material iscaused to adopt said first and second positions by fold forming alongfold lines which are prefabricated in the packaging material.
 3. Themethod as claimed in claim 1, wherein said enclosing step furthercomprises:producing the packaging containers from a web of packagingmaterial which is provided with the predefined crease lines facilitatingthe folding formation, reforming said web into a tube by unitinglongitudinal edges of the web with one another, and filling the thusformed tube with the intended contents, whereafter the tube, by repeatedflat-press- and sealing operations along narrow, mutually spaced apartsealing zones, is divided into individual packaging units which areseparated from the tube by incisions in said sealing zones; wherein saidseparate packaging containers are formed by folding along said creaselines such that the packaging containers are given the first containerposition defined by a first, flat or flattened shape when the packagingmaterial is folded along the crease lines and the packaging containersreceive a polygonal cross-section; said heat treating step furthercomprises introducing said separate packaging containers having saidfirst shape into an autoclave and heat-treating the packaging containersunder pressure such that a bacterial population in the contents and abacterial presence on a surface of the packaging material are reduced;and after the heat treatment, removing said packaging containers fromthe autoclave and raising said packaging containers to the secondcontainer position defined by a second, final shape by refolding thepackaging material along the crease lines so that some of said creaselines are included in a planar wall panel and the packaging containersare shaped into substantially parallelepipedic form by corner portionsbeing folded into triangular, double-walled flaps which are collapsed intowards and fixed at the side surfaces and/or bottom surfaces of thepackages.
 4. The method as claimed in claim 1, wherein the heat treatingstep includes positively compressing the packages for the purpose ofreducing the thickness of the packages.
 5. The method as claimed inclaim 1, wherein the packages include bag or cushion packages ofundefined geometric configuration which consist of cushions formed fromseparate sheets or webs of packaging material, in which said separatesheets or component materials of said separate webs are united along aninherently enclosed sealing joint or seam extending along the sheetedges, the first position of said cushion being attained when thecushion is placed in the treatment chamber in such a manner that saidsealing joint is substantially located in a horizontal plane.
 6. Themethod as claimed in claim 1, wherein the packages include packagingcontainers produced from punched blanks.
 7. The method as claimed inclaim 1, wherein the food is substantially homogeneous in its structureand is pumpable.
 8. The method as claimed in claim 1, wherein the heattreating is conducted as a continuous process in which the packagesintended for heat treatment are introduced into and removed from thetreatment chamber by means of sluice gates.
 9. An apparatus for carryingout the method as claimed in claim 1, comprising an autoclave includingone or more press devices, which, with the aid of drive means, may bemoved from an upper, inactive position to a lower, active position, saiddevices when disposed in the lower, active position compressing filledand closed packaging containers inserted into the autoclave for thepurpose of reducing the thickness of said containers during the heattreatment of the packages which is carried out in the autoclave.
 10. Themethod as claimed in claim 1, wherein the flexible or foldably formablematerial enables the manufacture of a rigid, dimensionally stablecontainer.